User agent stylesheet: a proposal

roger64 · 12-26-2014, 10:47 PM

Hi

I spotted an "anomaly" regarding the display of an image and after I checked its CSS with the Inspector, I discovered that this perceived "anomaly" was just the consequence of basic CSS rules. My EPUB had an incorporated but hidden "user agent stylesheet", and one of its values defeated my intended purpose... The only thing is that I was totally unaware of the UA values (here a 8px body margin).

I understand that the use of UA stylesheets is widespread and that they are quite useful to provide implicit values when our stylesheets do not provide any. But sometimes, they can give us trouble.

1. Does Calibre adds a "user agent stylesheet" to any EPUB, and if yes, according to which conditions?

2. The Inspector can detect these UA values but its use is not straightforward. Would it be possible to add somewhere a tick mark: "Display the content of user agent stylesheet"?

kovidgoyal · 12-26-2014, 10:57 PM

Where are you seeing this suer agent stylesheet exactly? Post a screenshot. calibre does not add anything to an EPUB while editing it.

EDIT: If you mean the default styling for elements that have no CSS applied, that is present in all EPUB readers, and its contents vary from reader to reader. It is not inserted into the EPUB, but is instead a property of the reader software. Whenever a HTML renderer encounters an HTML element with no styling applied, its basic style properties are taken from the suer agent stylesheet.

roger64 · 12-27-2014, 12:26 AM

Quote:

Originally Posted by kovidgoyal

Where are you seeing this suer agent stylesheet exactly? Post a screenshot. calibre does not add anything to an EPUB while editing it.

This is a screenshot of this EPUB as displayed using the Calibre editor.

http://pix.toile-libre.org/?img=1419657539.png

The Inspector is the only software which allowed me to understand what was happening.

If it can detect these interesting UA values, can it publish them somewhere?

kovidgoyal · 12-27-2014, 12:45 AM

There is no point, they are not fixed. They will vary from reader to reader and device to device and software version to software version. What Inspect shows you is particular to that version of WebKit. The values will be different in Adobe Digitqal Edition or indeed any other EPUB reading software.

roger64 · 12-27-2014, 02:00 AM

Thanks for your explanations.

12-26-2014, 10:47 PM	#1
roger64 Wizard Posts: 2,608 Karma: 3000161 Join Date: Jan 2009 Device: Kindle PW3 (wifi)	User agent stylesheet: a proposal Hi I spotted an "anomaly" regarding the display of an image and after I checked its CSS with the Inspector, I discovered that this perceived "anomaly" was just the consequence of basic CSS rules. My EPUB had an incorporated but hidden "user agent stylesheet", and one of its values defeated my intended purpose... The only thing is that I was totally unaware of the UA values (here a 8px body margin). I understand that the use of UA stylesheets is widespread and that they are quite useful to provide implicit values when our stylesheets do not provide any. But sometimes, they can give us trouble. 1. Does Calibre adds a "user agent stylesheet" to any EPUB, and if yes, according to which conditions? 2. The Inspector can detect these UA values but its use is not straightforward. Would it be possible to add somewhere a tick mark: "Display the content of user agent stylesheet"? Last edited by roger64; 12-26-2014 at 10:52 PM.

12-26-2014, 10:57 PM	#2
kovidgoyal creator of calibre Posts: 43,860 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Where are you seeing this suer agent stylesheet exactly? Post a screenshot. calibre does not add anything to an EPUB while editing it. EDIT: If you mean the default styling for elements that have no CSS applied, that is present in all EPUB readers, and its contents vary from reader to reader. It is not inserted into the EPUB, but is instead a property of the reader software. Whenever a HTML renderer encounters an HTML element with no styling applied, its basic style properties are taken from the suer agent stylesheet. Last edited by kovidgoyal; 12-26-2014 at 11:01 PM.

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12-27-2014, 12:45 AM	#4
kovidgoyal creator of calibre Posts: 43,860 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	There is no point, they are not fixed. They will vary from reader to reader and device to device and software version to software version. What Inspect shows you is particular to that version of WebKit. The values will be different in Adobe Digitqal Edition or indeed any other EPUB reading software.

12-27-2014, 02:00 AM	#5
roger64 Wizard Posts: 2,608 Karma: 3000161 Join Date: Jan 2009 Device: Kindle PW3 (wifi)	Thanks for your explanations.

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